This invention relates to MacPherson struts, and more particularly, the invention relates to an improved MacPherson strut with a "floating" striker plate mounted on the piston rod of the strut.
MacPherson struts have become commonplace elements of the suspensions of modern automobiles and related vehicles. Typically, such structures are used in the vehicle's front or steering suspension to support a "sprung" mass (i.e., the automobile body) upon an "unsprung" mass (i.e., the automobile chassis). The advantages of MacPherson struts in such applications are numerous and wellknown to the persons having skill in the art.
MacPherson struts used in the prior art have typically included a shock absorbing pressure cylinder contained within an outer strut cylinder with an attached piston and piston rod. Absorption of shock is accomplished by movement of the piston through fluids contained in the pressure cylinder in a manner wellknown in the art. A piston rod, attached to the piston, extends from the upper part of the pressure cylinder and is normally connected to the sprung mass (the automobile body) through a flexible connection to that mass. The strut cylinder is normally attached to the vehicle chassis at the cylinder's lower end, resulting in the strut being connected between the sprung and unsprung masses.
All MacPherson struts, including prior art struts, provide some arrangement for compensating for jounce (substantial jolt) that occurs when the vehicle encounters a severe surface irregularity. Without adequate precautions, such jounce can produce an impact between the automobile body and the top of the strut cylinder. The result of that impact can be severe damage to the strut assembly and the piston rod seal.
The prior art typically addressed this problem by providing a strut arrangement configured to protect the upper end of the strut cylinder and rod seal assembly. Normally, the upper ends of prior art cylinders are constructed with a removable body nut through which the piston rod extends to reach the automobile body. The body nut is typically threaded so that it can be screwed into the strut cylinder. The body nut also retains the piston rod seal, which provides a seal against loss of fluid from the cylinder during movement of the piston rod through the nut. To prevent damage from jounce, the body nut often includes a striker plate at its top and a compression or jounce bumper positioned around the piston rod above the striker plate.
Prior art striker plates are normally made of steel and are welded to the top of the body nut. Such striker plates have a central bore that surrounds the piston rod. When a severe irregularity in the travel surface is encountered by the vehicle's wheels, damage to the body and strut is minimized; the steel striker plate and the jounce bumper (usually made of a compressible material such as rubber) absorb the impact and prevents metal to metal contact and damage. Striker plates in the prior art are also often constructed to prevent water and other contaminants such as sand or dirt particles from being forced into the rod seal between the seal and the piston rod. Such contaminants, if allowed into the seal, would cause fluid leakage from the pressure cylinder and would damage the piston rod surface. Striker plates therefore normally provide a channel or similar structure that allows expulsion of water or other contaiminants that become trapped within the central bore of the striker plate. Without such a channel, the jounce bumper can act as a cap and piston combination, and cause dirt to enter the seal of the pressure cylinder.
While effective in protecting a conventional strut from normal shocks, the conventional striker plate and jounce bumper arrangement is not ideal. Use of a steel striker plate adds weight to the unsprung mass of the car, and adds to the complexity of the manufacturing operation due to the need to weld the striker plate to the body nut. An improved plate and the strut configuration is therefore desirable to reduce cost and weight, and to decrease the quantity and complexity of the strut's assembly operation.